Presumably, your HT receiver has high level outputs (RCA?) for the two front channels. These can be connected to your analog preamp inputs, perhaps "source #4 or whatever."
When you want to listen to your 2 channel sources, just select them and play them through your preamp.
When you want to listen to your 5.1 (or 7.1) HT material, just select "source #4 or whatever" on your analog preamp. Then your HT receiver will play your center and rear speakers while your two front speakers will be played by your 2 channel amp driven by your analog preamp which has been selected to the HT receiver as a source.
As Bob pointed out, you will need to adjust your analog preamp level to correctly balance the output volumes of the left and right front speakers.
This requires that your HT receiver has a high level output (like RCA) that can be connected to your analog preamp. And it requires an unused pair of inputs on your analog preamp.
When you want to listen to your 2 channel sources, just select them and play them through your preamp.
When you want to listen to your 5.1 (or 7.1) HT material, just select "source #4 or whatever" on your analog preamp. Then your HT receiver will play your center and rear speakers while your two front speakers will be played by your 2 channel amp driven by your analog preamp which has been selected to the HT receiver as a source.
As Bob pointed out, you will need to adjust your analog preamp level to correctly balance the output volumes of the left and right front speakers.
This requires that your HT receiver has a high level output (like RCA) that can be connected to your analog preamp. And it requires an unused pair of inputs on your analog preamp.